As data services gradually increase, the conventional Synchronous Digital Hierarchy (SDH) transmission technology has gained a progress correspondingly. The Next Generation SDH (NG SDH) technology, represented by the Virtual Concatenation, the Link Capacity Adjustment Scheme (LCAS) and the Generic Framing Procedure (GFP), has boosted the evolvement of a conventional SDH unit, which mainly provides Time Division Multiplexing (TDM) services, into a Multi-Service Transfer Platform (MSTP).
Meanwhile, in the field of data communication, requirements for operability and manageability are increasingly prominent. The Virtual Private Network (VPN) technology, particularly Layer 2 VPN (L2 VPN), has become the basic on which the data communication becomes operable. Accordingly, common L2 VPN technology includes Q-Tag (embedded)-in-Q-Tag (q-in-q), Multi-Protocol Label Switching (MPLS) L2 VPN, etc.
Here, the q-in-q is used for achieving the purpose of a separation between data streams of different users through using a tag in addition to the tag of Virtual Local Area Network (VLAN) as defined in the 802.1q.
In short, the MPLS L2 VPN differentiates between different data streams through encapsulating a user data packet and using a so-called label in the encapsulation so that a separation between the data streams of different users can be performed.
The above two technologies will be commonly referred to as L2 VPN label technology hereafter, unless indicated otherwise.
There are various implementation technologies to apply an L2 VPN service scheduling on the MSTP, dependent upon different system configurations.
FIG. 1 shows an L2 VPN-service scheduling method of prior art, in which services from between different line units and local Ethernet data services are scheduled on the same board by a cross-connecting unit.
FIG. 2 shows another L2 VPN-service scheduling method of prior art, which, in comparison with the method shown in FIG. 1, further includes a data exchanging plane to perform a data exchange between data service access processing units, however, the units connected with the cross-connecting unit are still the data service access processing units.
It is obvious from above that there exist the following disadvantages in the prior art.
1. The function of service access and the function of service scheduling are not separated from each other, and there is an absence of an independent service scheduling unit. In case data service access is not needed for a node, i.e., only the service scheduling is needed, the cost of the board for the data service access will be a waste.
2. In case there is a data service access at a data service interface, it is difficult for a data service access processing unit to achieve a “1+1” protection due to the limitation of the data service interface. Since the function of scheduling plays a very important role in a network, and a redundant protection is almost compulsively required, and such drawback is rather serious.